I often use fred in short demos as the name of a variable or as a function name.
Because I am lazy and the letters f r e d are right next to each other on the keyboard.
If I need another name I often use d e r f which is fred backwards.
On a side note: I have happy memories associated with the name Fred.
"Right said Fred" is a joke/novelty song written by Ted Dicks and Myles Rudge in 1962. Sung by the gently wonderful Mr Bernard Cribbins.
Forgive an old man for gathering happy memories and wanting to share some of them